Lecture 19- Pain

Question 1

What is nociception?

Answer 1

-activation of nociceptive primary afferents

Question 2

What is pain?

Answer 2

-conscious, affective unpleasant somaesthic percept localized to the body

Question 3

What is hyperalgesia?

Answer 3

-increased sensitivity to noxious stimuli

Question 4

Does nociception have specialised neurons?

Answer 4

-yes

Question 5

How can you map the receptive fields of nociception neurons?

Answer 5

-with heat

Question 6

What is the pattern of response of nociception afferents?

Answer 6

• do not respond till sth really happens
• high threshold
• can be chemical burn too (whereas mechanorecpetors are very sensitive)
• only starts to fire at 45 degrees then at 60 degrees very repsonsive but the non-nociceptive thermoreceptor plateus
• nociceptors= encode for temps etc that damage, opposed to other recpetors

Question 7

What are the two categories of pain?

Answer 7

• first (sharp pain)
• second (duller, burning pain)

Question 8

What pain do the A delta fiber convey?

Answer 8

-small thinly myelinated fibres, 5 microns= fast sharp pain (mechanosensors at high threshold)

Question 9

What pain do C fibres convey?

Answer 9

thinnest nerve fibres - unmyelinated= C fiber (here myelin would slow it down if it were here due to the small size) -1 micron= sensation of diffuse, duller burning pain -the C fibres are polymodal= respond to noxius chemical and mechanical stress when very high, respond to proton concentration (acidity)

Question 10

What is the most common peripheral nerve fibre?

Answer 10

C fibres -small and everywhere

Question 11

What are the characteristics of C fibres?

Answer 11

-0.2-1.5 micometers -0.5-2.0 meters for second speed -temperature, pain, itch

Question 12

What are the characteristics of A delta fibres?

Answer 12

-myelinated -1-5 micrometers diameter -5-30 M/s -pain and temperature

Question 13

What are the characteristics of A beta fibres?

Answer 13

-6-12 micrometers diameter -35-75m/s -mechanoreceptors of skin

Question 14

What are the characteristics of A alpha fibres?

Answer 14

-13-20 micrometers in diameter -80-120m/s -proprioceptors od skeletal muscle

Question 15

Where does capsaicin bind?

Answer 15

-can diffuse through the membrane so it binds on the inside -VR-1 receptor

Question 16

What binds to VR-1 receptor?

Answer 16

-capsaicin -heat and H+ (acidity)

Question 17

What is capsaicin in?

Answer 17

-jalapeno -red chilli -habanero

Question 18

What is the nociception pathway like?

Answer 18

-cell body in dorsal root ganglia -small cell bodies -do their transmitting locally (segment or two) find their target cell in the superficial dorsal horn -crosses over right away -the second neuron goes to the thalamus

Question 19

How is the nociception pathway different from the touch pathway?

Answer 19

-very different to the touch pathway wher eit was on the same side till brain stem -here it crosses over right away

Question 20

What is the spinalthalamic tract?

Answer 20

-the nociception pathway -also called anterior lateral system (ALS)

Question 21

Where in the spine do the C fibres terminate?

Answer 21

• in the superficial dorsal horn(the purple)
• in the marginal zone or substantia gelatinosa

Question 22

Where in the spine do A delta fibres terminate?

Answer 22

can terminate in areas further away = even in the base of the dorsal horn as well as the superficial basal horn

Question 23

Is there mixing of information from nociception afferents in the spinal cord?

Answer 23

-yes -one cell body can get information from A delta as well as C fibre

Question 24

What would happen if your spinal cord was cut in half of its width?

Answer 24

• feel only one side of the body
• lose nociception on one side and touch on the other
• nociception intact on one side as it crosses over locally
• the touch pathway stays on one side whereas the pain crosses over right away
• brown sicard syndrom

Question 25

What are the two main pathways of the anterolateral system?

Answer 25

1.Sensory-discriminative(the one to somatosensory cortex) 2.Affective-motivational (the one to insular and anterior cingulate cortex)

Question 26

What is the anterolateral system pathway (detail)?

Answer 26

• from the spine goes to different parts of the brainstem/forebrain
• first division is to ventral posterior nucleus in the thalamus to the somatosensory S1 and S2
• second division goes to the amygdala, hypothalamus, periaquiductal grey, superior colliculus, reticular formation
• third division goes to the midline thalamic nuclei and from there to the insular cortex and anterior cingulate cortex

Question 27

What are the functions of the anterolateral system pathway?

Answer 27

-the one to the insularn cortex and anterior cingulate cortex is the pahtway of how it feels, motivational and connected to learning -the one to the amygdala etc. is about the emotional feelings associated with pain -the one going to the somatosensory cortex, this is how we can tell where sth hurts, can loacte it

Question 28

Where is the cingulate cortex?

Answer 28

anterior cingulate cortex (blue)= where the last neuron from the nociceptors ends (the third goes from brain stem to here)

-lot of emotional states include this cortex (hunger, thirst)

Question 29

Where is the insular cortex?

Answer 29

• more cortex again after removing he upper bit of the cortex
• get lot of receptor input, from organs

Question 30

What is the nociception pathway mediating discriminative aspects of temperature like for the body(picture)?

Answer 30

-

Question 31

What is the nociception pathway mediating discriminative aspects of temperature like for the face (picture)?

Answer 31

trigeminal nucleus= pain and temp from the face and head

Question 32

What is the trigeminal nucleus for?

Answer 32

trigeminal nucleus= pain and temp from the face and head

Question 33

What appears in the tissue when tissue damage?

Answer 33

-bradykinin= when damage in cells -ATP= leaks when cell damage -more acidic environment -histamine -prostaglandin

Question 34

What activates C fibres?

Answer 34

-presence of bradykinin, increase in ATP, 5-HT(serotonin),prostaglandin,histamine

Question 35

What is the reflex within C fibres?

Answer 35

• reflex= within branches of this fibre
• nerve impulse to other branches and release substance P (peptide) and CGRP=dilation of blood vessels
• red because of inflammation
• positive feedback effect= activation leads to more activation in the other terminals

Question 36

Is pain a homeostatic system?

Answer 36

-yes! maintaining integrity of the skin

Question 37

What are phantom limbs?

Answer 37

-part of the body removed but they still feel like it’s there -ther is not a nerve saying this is your limb= this is constructed in the brain and that can exist without the mechanoreceptors

Question 38

What are the descending systems that modulate the transmission of ascending pain signals?

Answer 38

• originates in the somatosensory cortex
• the raphe nuclei and all that line is in the brain stem! they project to the spinal cord to the first synapse in the anterolateral system

Question 39

What happens at the first synapse of the anterolateral system when being modulated by ascending systems?

Answer 39

• this is how pain reduction occurs
• driven by cortical areas
• enkephalins are peptides

Question 40

What is the dorsal column pathway fro visceral pain like?

Answer 40

• goes from the gut etc. to the spinal cord
• then synapses in the medulla and goes to the ventral posterior nuclear complex of the thalamus
• from there goes to the insular cortex
• in the medulla crosses over in the medial lemniscus

Question 41

Is the idea of a pain pathway an oversimplification?

Answer 41

-yes